Why You Wake Up Wide Awake Between 2 AM and 4 AM... And Why You Shouldn't Sleep Right After Working Late

[Anchor]

Do you ever find yourself waking up for no apparent reason between 2 AM and 4 AM? Once you are awake, it is naturally difficult to fall back into a deep sleep. Let's find out why we frequently wake up in the middle of the night and how we can get a sound sleep.

[Reporter]

There are definitely factors involved, such as the autonomic nervous system or stress-related hormones.

The autonomic nervous system plays a role in detecting threats and arousing the brain.

Think back to prehistoric times when a lion might threaten you while you were sleeping at any moment. In such dangerous situations, even the slightest rustling sound would cause you to wake up.

There is a clear reason why people wake up due to hyperarousal of the brain, driven by an increase in stress hormones, an overactive sympathetic nervous system, or a drop in the parasympathetic nervous system.

Cause ① Stress

I experience this too, and many people face serious issues when they are sick, stressed, or worried—such as having trouble falling asleep, waking up early in the morning and struggling to fall back asleep, or waking up far too early.

There is a stress hormone called cortisol, which should be secreted during the day and suppressed at night to help you sleep.

If you are under a lot of stress and tense, stress hormones are secreted even while you sleep.

Because an increase in stress hormones and the activation of the sympathetic nervous system happen together, there are actually quite a few people who wake up sweating or experiencing heart palpitations in the middle of the night. Simply put, they end up worrying about their concerns even in their dreams.

Cause ② Sleep Apnea

Among patients actually treated in hospitals, the number one cause is sleep apnea.

It is commonly found in middle-aged individuals, especially men after their 40s. For those with thick necks or sudden weight gain, their airway tends to narrow repeatedly during sleep.

Because breathing is blocked during sleep, the brain naturally has to wake up so that tension can be applied to the airway. Consequently, they cannot achieve deep sleep.

Cause ③ Delayed Sleep Phase Syndrome

One common cause among young people is something called delayed sleep phase syndrome.

Normally, melatonin is widely secreted around 12 AM to help induce sleep, and waking up should occur at 6 AM to 7 AM. However, the secretion is delayed until around 3 AM to 4 AM and continues until 10 AM to 11 AM, shifting backward.

When this shift happens, fatigue accumulates during the day when you need to go to work, leading you to fall into a light sleep at night and wake up early in the morning. However, if this bounces back and forth irregularly due to lifestyle habits—such as sleeping and waking up late or sleeping and waking up early—sleep hormones fail to be secreted consistently.

If you work late, going straight to bed is generally not recommended. Why? Because when you work, you become excited. As mentioned earlier, the autonomic and sympathetic nervous systems become activated, and stress hormones like cortisol increase. You need to let your excited nervous system settle for at least an hour or two after coming home from work before going to sleep to achieve deep sleep. Yet, because you worked late and are tired, you rush into sleep like you are pressed for time, and as soon as your immediate need for sleep is met, you wake right back up.

Sleep deprivation is considered unconditionally bad. You can think of it as increasing the risk of all kinds of illnesses. There is something called the glymphatic system. It is a brain-cleansing process that takes place during sleep. That happens while you sleep, and it occurs more in the latter half of sleep than in the first half.

You can think of the early part of sleep as a time for the brain and body to rest, while the latter half is a time for the brain to wake up again, actively clean itself, and regenerate. If you frequently wake up in the middle of the night and your total sleep time decreases, the latter half of your sleep will become deficient, which in turn accelerates brain aging.

The most important factor is consistency. Due to occupational reasons, that is often difficult to maintain, but you still need to design your schedule with that in mind.

Because people lack sleep during weekdays, they commonly tend to sleep in until 11 AM or 12 PM on weekends. Sleeping late and pushing back your sleep schedule to 2 AM, 3 AM, or 4 AM just because it is the weekend is the worst thing you can do. It is called social jetlag—the time difference between weekdays and weekends. Textbook guidelines recommend keeping it within 1 to 2 hours.

The second most important factor is light. The melatonin cycle is most heavily influenced by light.

What should you do before going to bed? Keep it dark. Simply refraining from bringing your smartphone into the bed will greatly improve your sleep.

Additionally, exercising certainly helps. I exercise a lot, walking 10,000 steps a day. In fact, what I recommend is strength training. Substances released during muscle workouts are known to have a very positive impact on our sleep.

How can you tell if your situation is serious enough to make you think, "Am I in serious trouble? Should I go see a doctor?"

The first criterion to check is whether your sleep problems are severely interfering with your work during the day, causing functional impairment. The second criterion is anticipatory anxiety—feeling anxious even before going to bed out of fear that you might wake up in the middle of the night again. That is a negative sign. If this repeats for 2 or 3 days a week or more, you should consider seeking professional help.

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